| The efficient treatment of landfill leachate has always been a problem that people pay close attention to.With the extension of the landfill time,the biodegradable organic matter in the landfill leachate gradually decreases,and the concentration of ammonia nitrogen continues to rise,gradually forming the late landfill leachate.Due to the poor biodegradability of the late landfill leachate,it is difficult to remove nitrogen in the biochemical treatment process,and it also faces key issues such as the control of the dosage of carbon sources and the selection of types.In addition,the leachate is rich in antibiotic resistance genes(ARGs)that are easy to spread.The changes and impact characteristics of the late landfill leachate during the treatment process are not clear.Whether the changes during the treatment process will be affected by the carbon source is also not clear.Based on these,this study relied on two sets of reactors for the treatment of late leachate in the laboratory,using high-throughput sequencing and fluorescent quantitative PCR to study the effects of different nitrification methods and different carbon sources on the denitrification performance of late leachate,and using carbon sources to optimize the C/N ratio of influent water and membrane technology to efficiently treat the late leachate,and elucidate the denitrification mechanism from the aspects of microbial community and functional genes,and discuss the changes and removal characteristics of ARGs during the treatment process.The main research results of this paper are as follows:1.The effect of different nitrification methods and carbon source types on the denitrification performance of late landfill leachateIn the SBR reactor,continuous aeration can be used to achieve whole nitrification(WN);while intermittent aeration is a strategy to quickly achieve partial nitrification(PN).Compared with PN,WN has a higher WN under the same conditions.Denitrification and carbon removal effect,but consumes a higher amount of aeration.In this simulation process,partial denitrification(PD)saves about 30%of the carbon source dosage compared with whole denitrification(WD).From the point of view of the degradation rate of nitrate and nitrite in a single denitrification cycle in this experiment,sodium acetate>methanol>glucose.When the carbon source is sufficient or appropriate,the three denitrification carbon sources have no significant effect on the TN removal rate(P>0.05),and all can reach more than 76%.From the analysis of the economic benefits of carbon sources,the most economical is the addition of methanol,the operating cost is 7.56 yuan/m~3,followed by glucose and sodium acetate,which are 15.90 and 20.63 yuan/m~3 respectively.Candidatus＿Competibacter is a specific denitrifying glycan bacteria of the glucose group,but it may cause sludge swelling;the high denitrification rate of sodium acetate may be attributed to the enrichment of Thaurea and Truepera;and the rapid propagation of WS6＿(Dojkabacteria)may cause the sludge acclimatization period longer after methanol is added,and it is the reason for the"adaptation period"in the early denitrification.2.Carbon source optimization research on the denitrification performance of the MBR process of late landfill leachateTwo different methods are used—adding a single carbon source(TY)and adding fresh leachate(HH)combined with MBR membrane process to treat the late leachate.When HRT is about 3 days,the TN removal rate is 80.2%and 78.7%respectively.The total nitrogen basically meets the effluent requirements of the biochemical section of the leachate process,but the COD of the TY group effluent is difficult to meet the standard.The membrane fouling of the HH group is more serious,and membrane cleaning can promote the denitrification and carbon removal ability of the reactor.Truepera and Paracoccus are abundantly enriched in HH group,which is the reason why the ammonia nitrogen removal rate of HH group is significantly higher than that of TY group at the lower stage of influent C/N.The high COD treatment rate of the HH group may be closely related to the degradation of macromolecular organics by Saccharimonadales and Acinetobacter.In the MBR reactor,AOB-amoA is the dominant nitrification gene,and higher dissolved oxygen may have an inhibitory effect on AOA-amoA.The laboratory MBR system mainly relies on AOA,AOB and nirK denitrifying bacteria for denitrification.The intrinsic relationship between AOA,nirS and nosZ makes them linked in the denitrification process and promotes the generation of denitrification pathways.The host microorganisms of each functional gene are diverse.The amoA gene may exist in Nitrosomonas or in a variety of denitrifying bacteria.Paracoccus may be the main host microorganism of nirK,and it is the key to improving denitrification efficiency.3.Study on the change characteristics of ARGs during the treatment of late landfill leachate by carbon source regulationAfter the adjustment tank,ultrafiltration,and nanofiltration stages,the ARGs abundance value of the effluent in the actual process showed a downward trend.The highest reduction stage is the ultrafiltration effluent after the MBR biochemical section.The reduction rate is higher than that of the adjustment tank.80%.The partial nitrification process in the laboratory has a significant reduction effect on various ARGs.In addition to erm B,the ARGs in denitrification reactors with different carbon sources are also reduced accordingly.ARGs are also closely related to the amount of carbon source added.For example,ermB,sul1 and integrase genes are greatly affected by the amount of carbon source.The laboratory MBR reactor is selective for the reduction of ARGs in the late leachate.The change of host microorganisms is the main driving factor for the migration and transformation of ARGs.Pusillimonas,Leucobacter and Pseudohongiella may be the main host microorganisms for many ARGs in the late leachate.In summary,partial nitrification and denitrification has the advantage of saving carbon sources compared to whole nitrification and denitrification.The three different carbon sources have their own advantages and disadvantages in terms of cost,safety and stability,but they all have good performance in denitrification.MBR process can solve the problem of instability of effluent in the biochemical stage.The method of co-injection of late and fresh leachate has more advantages in effluent carbon compliance;the partial nitrification process and the denitrification process with the addition of different carbon sources are conducive to the reduction of ARGs.And it is also closely related to the amount of carbon source added.The MBR reactor is selective in the reduction of ARGs.The change of microbial flora is the main driving force affecting the change of ARGs.This study can provide technical and theoretical guidance for the optimization of the treatment process of the late leachate and the control of the antibiotic resistance gene pollution. |
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